How Advanced Ozone Cleaning Reduces Chemical and Solvent Usage

As environmental concerns mount and regulatory compliance becomes more difficult, companies that reduce the use of hazardous chemicals and solvents will have a competitive advantage. In addition to reducing costs, the use of fewer corrosive chemicals improves workplace safety and can lead to better semiconductor manufacturing facility performance. Modutek’s patented advanced ozone cleaning process saves money and reduces the contaminating particle count on wafer surfaces. Depending on process requirements, ozone cleaning can out-perform traditional wafer cleaning with harsh chemicals. Modutek’s ozone cleaning process is compact, fast, and safe.

Advanced Ozone Cleaning Converts Organic Impurities to Carbon Dioxide

Modutek has developed the Cold Strip sub ambient process that operates with deionized water and the Organostrip process that uses a mild acid at room temperature for photo resist strip. This also eliminates the use of NMP solvent base strippers. Both use ozone to clean organic contaminants from wafer surfaces and both leave harmless residues that allow for disposal without special neutralizing procedures.

The Cold Strip Advanced Ozone Cleaning Process operates at four to ten degrees centigrade and uses deionized water to strip silicon wafers of water-soluble inorganic impurities. After the wafers are rinsed with deionized water, ozone is introduced into the chamber. The ozone reacts with the remaining organic impurities and converts them to carbon dioxide. Particle contamination is reduced as well because the ozone reacts with organic particles. Wafers are more effectively cleaned with a reduced particle count.

In the Organostrip process, wafers are rinsed with a solution of a mild acid and ozone at room temperature. The acid has a high ozone solubility that lets the ozonated solution remove organic compounds from the wafer surfaces quickly and completely. The process is compatible with metals such as gold, copper, and aluminum, and the waste products of the Organostrip process are not hazardous.

Modutek uses its DryZone solvent gradient dryer for the Advanced Ozone Cleaning Process that the company developed to address customer concerns. Customers experienced high particle counts and issues with the use of hazardous chemicals, including their effect on the environment. The developed process successfully addresses these issues and delivers effective wafer cleaning.

Modutek’s Advanced Ozone Cleaning Process Provides Substantial Benefits

Modutek developed the Advanced Ozone Cleaning Process to address specific customer concerns, but the Cold Strip and Organostrip processes also improve wafer cleaning and facility operations. The benefits of using ozone cleaning include the following:

  • Reduced cost for process chemicals. The acids used in a traditional wafer cleaning process, such as sulfuric or hydrochloric acids, are expensive, and the cleaning processes such as Piranha clean use substantial volumes of chemicals. Ozone and the mild acids or solvents used in ozone clean are less expensive and the solutions last longer.
  • Reduced cost for chemical handling. The storage, delivery, and disposal of hazardous chemicals used for traditional wafer cleaning is expensive. The handling of ozone and the mild chemicals used for ozone cleaning requires no special measures.
  • Improved workplace safety. The chemical baths used for traditional wafer cleaning often operate at high temperatures and they can be dangerous. The ozone cleaning process chemicals are safe and the operation is done at sub ambient or at room temperature.
  • Higher throughput. Advanced ozone cleaning takes less time than traditional cleaning methods.
  • Improved yields. Ozone cleaning reduces particle counts and results in higher output quality with fewer product defects.

Modutek’s Continued Process Improvement Delivers Innovative Solutions for Customers

Modutek works closely with customers to identify new concerns and solve existing processing problems. Using extensive in-house experience and expertise in wet process technology allows Modutek to provide innovative solutions to meet customer needs. New wet process steps such as Advanced Ozone Cleaning can help customers improve semiconductor manufacturing facility performance and increase profitability.

How Better KOH Etching Results Are Achieved Using Teflon Tanks

While KOH etching is widely used, the process controls and the process tanks can play a major role in obtaining the desired results. Improved KOH etching means precise control of the etch rate and a low particle count. When the etch rate is exact and consistent, the etched shapes in the silicon wafer will be as specified and the final semiconductor product will function as expected. When particle counts are low, the number of defective products will go down and yield will increase. Combining Teflon tanks with high-precision control systems can deliver superior etching results while reducing waste and increasing output quality.

How KOH Etching Can Be Controlled and Improved

KOH etching uses a solution of potassium hydroxide to etch silicon wafers. The etch rate is influenced by the bath temperature, the concentration of potassium hydroxide, the orientation of the silicon crystal lattice, and possible doping of the silicon. Each of these factors helps determine how quickly etching proceeds in the horizontal and vertical directions.

The cubic crystal lattice of the silicon has different atom densities in different directions. The wafer can be oriented in such a way that etching proceeds more quickly in a given direction. Doping, or adding impurities to the silicon, can be used to stop the etching at a particular location in the wafer. While both these factors can influence the etch rate and the microscopic silicon structures, they are fixed before the etching process begins.

Because the etch rate partly depends on the KOH concentration, it is critical to add the right amount of KOH to water. An accurate chemical delivery system can help ensure that the etching tank contains the right solution concentration before the etching process starts.

The etch rate speeds up with an increasing temperature. This means that the tank and solution temperature must be raised quickly to the specified level and must be maintained precisely at the set point for the duration of the etching process. Accurate temperature control is important for improved etching performance.

Modutek’s Teflon Tanks and Controls Help Achieve Better Etching Results

Modutek provides temperature-controlled Teflon tanks and precise chemical delivery systems needed for excellent etching rate control for improved KOH etching results. These two process variables determine the KOH etch rate once the doped silicon wafer is placed in the process tank with the correct lattice orientation. After the etching process begins, the temperature becomes the critical factor in obtaining the desired etching results.

Modutek’s Teflon tanks are designed to minimize particle contamination and deliver fast heating with accurate temperature control. The tanks have an all-Teflon liquid path and are available in circulating or static models. The heater can be located in the overflow weir or inline. Even heating throughout the tanks ensures that the etching rate is the same everywhere.

To facilitate etch rate control, Modutek’s Teflon tanks heat up quickly at a rate of 2 to 3 degrees centigrade per minute. Once the set point is reached, the temperature controller maintains the temperature at plus or minus 0.5 degrees centigrade. The tanks can operate at 30 to 100 degrees centigrade and temperature and level limit settings can be applied. KOH etching proceeds quickly and reliably to produce the desired microscopic silicon structures.

Modutek Designs Teflon Tanks to Match Customer Requirements

Modutek’s in-house team works closely with customers to ensure that their wet process equipment meets their needs. While standard Teflon tanks are available, Modutek will design and build custom sizes with special features as required. Whether standard or custom designs, the high-quality materials, and precision controls ensure that KOH etch results satisfy even the most demanding requirements and that the Teflon tanks deliver the expected performance. For a free quote or consultation to discuss your specific process requirements contact us or call 866-803-1533.